Various sealing elements, for example in the form of a single layer or liner, are utilized to maintain the integrity of a container such as for liquid or dry food stuff applications, medical products, and nutritional products. Single layer sealing elements can be formed by extruding a polymer composition, cutting and placing a quantity of the extrudate at a desired location such as in the center of a cap, followed by compression molding the extrudate into a gasket or liner. In other embodiments, injection molding can be utilized to produce a sealing element in the form of a seal ring, for example in a cap.
Properties required of the sealing elements can vary depending upon individual applications. In some embodiments, sealing elements are required to maintain a suitable oxygen barrier for a desired lifespan of the product and also be easily removable from the container when desired by a consumer or other user. The sealing elements also should provide adequate sealing at a wide range of temperatures. Some sealing elements must be resistant to acids or bases. Further, sealing elements whether designed for a single use or a multiple use item, should retain their integrity and not shred or tear in order to prevent contamination of the packaged products.
International publication WO 02/141171 relates to a liner with reportedly improved oxygen barrier properties for use with closure cap shells. The liners are made of a composition that includes a thermoplastic elastomer, polyisobutylene and polybutylene. The publication further states that oil-based plasticizers, such as mineral oil have been included in liner compositions to improve the processability of the composition. However, under certain conditions, extractable compounds from the mineral oil have been known to migrate from the liner composition to the stored food product, according to the publication. Plasticizers such as mineral oil have also been known to exhibit an odor and/or affect the taste of the food product. Further, it is stated that it would be desirable to provide a liner that is easy to process but (1) does not include an oil or other plasticizer, (2) does not affect the taste of the stored food product, and (3) is substantially odorless.
U.S. Pat. No. 7,056,971 relates to a thermoplastic elastomer which is oxygen-permeable that is provided with reportedly excellent barrier properties against oxygen by melt-blending with a liquid polyisobutene oil plasticizer in an amount insufficient to render the plasticized elastomer tacky. It is further stated that polybutene, whether homo- or copolymers of isobutene, 1-butene (α-butylene) and/or 2-butene (β-butylene, whether cis- or trans-) irrespective of the ratio of the repeating units, and polymers of higher alkenes having from 5 to about 8 carbon atoms (“poly(higher)alkenes”), are typically rubbery solids. But such rubbers, it is stated, by themselves have unsatisfactorily high oxygen-permeation rates. Since a thin seal of an adequately deformable block copolymer, formed of S-blocks and a M-block of a conjugated diene, or, of a mono(lower)olefin, and no harder than Shore A 90, provides an unsatisfactorily high oxygen-permeation rate, it is reportedly not surprising that a rubbery poly(higher)alkene would also provide a comparably unsatisfactory oxygen-permeation rate.
A problem still exists as thermoplastic elastomer sealing elements are needed which have desirable barrier properties, that are readily processable under desired conditions, also do not contribute to one or more of taste and odor of the packaged product, and which are especially useful in foodstuff applications. Silicone oil, although it is effective in reducing removal torque, can cause reduced barrier performance and bondability to cap substrate. Fatty amides suitable for reducing tackiness have unsaturation, which is prone to oxidation/degradation and formation of odorous chemicals. When fatty amides are used in more than 10-20 phr, the composition is not suitable for food contact application due to sensory problems. When relatively high MW polyisobutylene is used, the compounds with fatty amides or silicone oil as lubricant are also difficult to process due to increase melt viscosity.